OFFSET
1,2
COMMENTS
These are all primorial numbers (A002110).
It appears that the primorial index of a(n) is A256968(n-1) for n>=1. - Michel Marcus, Oct 07 2019
LINKS
Eric Weisstein's World of Mathematics, Totient Function
MATHEMATICA
Table[prod=1; i=0; While[prod<n, i++; prod=prod/(1-1/Prime[i])]; Times@@Prime[Range[i]], {n, 1, 9}]
PROG
(PARI) a(n) = my(p=1, i=0); while(p<n, i++; p = p/(1-1/prime(i))); prod(k=1, i, prime(k)); \\ Michel Marcus, Oct 07 2019
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
T. D. Noe, Jan 09 2004
STATUS
approved